Fuel and air purge system for diaphragm carburetors

Abstract

A method of reducing gaseous phase presence in the liquid fuel metering chamber of a diaphragm by providing a "High-Point Pick Up" hole positioned in the optimal metering chamber location (highest) to assure maximum purge evacuation of air and/or other gases prior to engine start-up and during running. This optimal location is dependent upon first determining, in advance of carburetor fuel feed circuitry and/or air purge system design, the orientation of the carburetor as mounted on the engine in its primary operator usage position, or so-called "standard operating position" (SOP). This SOP in turn is determined in the first instance by the engine manufacturer and/or the manufacturer of the portable engine-driven handheld appliance on which the engine is mounted. In one embodiment the two typical fluid circuits (air purge and normal idle/high speed fuel feed circuits) share a common, sole take-off inlet opening into the metering chamber, the same being located at the highest elevation point in the metering chamber in the given SOP orientation. This assures that the maximum amount of air and/or fuel vapor is removed from the metering chamber during purging prior to start-up and during running. In accordance with the invention, the primary usage position (SOP orientation) of the engine is determined and becomes a known use parameter prior to the carburetor manufacturer determining such take-off hole location. Both butterfly valve cubic carburetor and rotary valve carburetor embodiments are disclosed embodying the invention.

I claim:  
     
       1. A method of reducing gaseous phase presence in the liquid fuel metering chamber of a diaphragm carburetor for an internal combustion engine, such phase being in the form of air or fuel vapor agglomeration and/or bubble growth due to the same evaporating or effervescing from the liquid fuel during engine running and/or in the form of air when the chamber is not full of liquid fuel and hence air-filled due to carburetor fuel drain-down after engine-shut down, said method comprising the steps of: 
       (a) providing a diaphragm type carburetor having a main air/fuel mixing through passageway, a fuel metering cavity formed in a carburetor body part and a metering diaphragm spanning said metering cavity and defining a fuel metering chamber therebetween, a liquid fuel supply passageway coupled between a pressurized source of liquid fuel and said metering chamber, an inlet valve disposed in said supply passage and being operably coupled to the diaphragm for controlling opening and closing of said inlet valve to admit pressurized liquid fuel from the fuel source to the metering chamber in response to pressure differential between atmospheric pressure and engine-intake-induced negative pressure in the carburetor mixing passageway acting on the metering diaphragm, an engine fuel feed metering circuit passageway system having a first inlet operably communicating with the metering chamber and outlet means operably communicating via check valve means with the carburetor mixing passageway for supplying and metering liquid fuel from the metering chamber via the outlet means into the mixing passageway to form therein an air/fuel mixture for operating the engine, and an air purge passageway system including a fuel vapor and air purge passageway having a second inlet operably communicating with the metering chamber and an outlet adapted for operably communicating with a return line leading to the fuel source, said air purge passageway system also including a pump and associated intake and outlet valves operably coupled in said purge passageway for pumping gas and/or liquid from the metering chamber into the return line,  
       (b) determining what will be the highest elevation region in the metering chamber with the carburetor mounted on the engine and the mounted carburetor and engine together being oriented in the standard operating position of the engine, and  
       (c) locating said first and second passageway inlets to communicate with said highest elevation region of the metering chamber to thereby insure that substantially all such gaseous phase presence is removed from the metering chamber by operation of the passageway systems associated with said inlets at least when said engine is oriented in the standard operating position.  
     
     
       2. The method of  claim 1  wherein said first and second inlets are constructed to communicate solely with a single common inlet opening directly into the highest elevation region of the metering chamber such that operation of said purge system, before starting the engine, removes substantially all gaseous phase metering chamber contents from the metering chamber and the fuel feed circuit while drawing liquid fuel into the metering chamber to thereby condition the carburetor for engine start-up with the engine oriented in the standard operating position, and such that while the engine is running in the standard operating position, the gaseous phase bubbles released from the liquid fuel, while resident in the metering chamber, are not allowed to become large enough, either singly or by agglomeration, to adversely affect engine performance when they are drawn into the engine via the fuel feed circuit. 
     
     
       3. The method set forth in  claim 1  wherein the engine comprises a mini-four-stroke-cycle single cylinder engine having an engine displacement in the order of 20 to 35 cc and being adapted for use on a hand-held engine-driven appliance such as a weed-trimmer or the like. 
     
     
       4. The method set forth in  claim 2  wherein said air purge pump comprises a manually operable squeeze bulb operably associated with said pump inlet and outlet valves and defining the variable volume pumping chamber of the air purge system. 
     
     
       5. The method set forth in  claim 4  wherein said squeeze bulb is mounted on said carburetor. 
     
     
       6. The method of  claim 1  wherein the outlet means of the engine fuel feed metering circuit passageway system includes both idle and high speed outlet fuel feeding orifice means both communicating with the metering chamber solely via the first inlet of the fuel feed metering circuit passageway system. 
     
     
       7. The method of  claim 6  wherein said first and second inlets are constructed to communicate solely with a single common inlet opening directly into the highest elevation region of the metering chamber such that operation of said purge system, before starting the engine, removes substantially all gaseous phase metering chamber contents from the metering chamber while drawing liquid fuel into the metering chamber to thereby condition the carburetor for engine start-up with the engine oriented in the standard operating position, and such that while the engine is running in the standard operating position, the gaseous phase bubbles released from the liquid fuel, while resident in the metering chamber, are not allowed to become large enough, either singly or by agglomeration, to adversely affect engine performance when they are drawn into the engine via the fuel feed circuit. 
     
     
       8. The method of  claim 7  wherein the engine comprises a mini-four-stroke-cycle single cylinder engine having an engine displacement in the order of 20 to 35 cc and being adapted for use on a hand-held engine-driven appliance such as a weed-trimmer or the like. 
     
     
       9. A method of reducing gaseous phase presence in the liquid fuel metering chamber of a diaphragm carburetor for an internal combustion engine, such phase being in the form of air or fuel vapor agglomeration and/or bubble growth due to the same evaporating or effervescing from the liquid fuel during engine running, said method comprising the steps of: 
       (a) providing a diaphragm type carburetor having a main air/fuel mixing through passageway, a fuel metering cavity formed in a carburetor body part and a metering diaphragm spanning said metering cavity and defining a fuel metering chamber therebetween, a liquid fuel supply passageway coupled between a pressurized source of liquid fuel and said metering chamber, an inlet valve disposed in said supply passage and being operably coupled to the diaphragm for controlling opening and closing of said inlet valve to admit pressurized liquid fuel from the fuel source to the metering chamber in response to pressure differential between atmospheric pressure and engine-intake-induced negative pressure in the carburetor mixing passageway acting on the metering diaphragm, an engine fuel feed metering circuit passageway system having a first inlet operably communicating with the metering chamber and outlet means operably communicating via check valve means with the carburetor mixing passageway for supplying and metering liquid fuel from the metering chamber via the outlet means into the mixing passageway to form therein an air/fuel mixture for operating the engine,  
       (b) determining what will be the highest elevation region in the metering chamber with the carburetor mounted on the engine and the mounted carburetor and engine together being oriented in the standard operating position of the engine, and  
       (c) locating said first passageway inlet to communicate with said highest elevation region of the metering chamber to thereby insure that substantially all such gaseous phase presence is removed from the metering chamber by operation of the engine fuel feed circuit passageway system associated with said first inlet whereby while the engine is running in the standard operating position the gaseous phase bubbles released from the liquid fuel, while resident in the metering chamber, are not allowed to become large enough, either singly or by agglomeration, to adversely affect engine performance when they are drawn into the engine via the fuel feed circuit.  
     
     
       10. The method set forth in  claim 1  wherein the engine comprises a mini-four stroke cycle single cylinder engine having an engine displacement in the order of 20 to 35 cc and being adapted for use on a hand-held engine-driven appliance such as a weed-trimmer or the like. 
     
     
       11. The method of  claim 9  wherein the outlet means of the engine fuel feed metering circuit passageway system includes both idle and high speed outlet fuel feeding orifice means both communicating with the metering chamber solely via the first inlet of the fuel feed metering circuit passageway system. 
     
     
       12. The method of  claim 11  wherein the engine comprises a mini-four-stroke-cycle single cylinder engine having an engine displacement in the order of 20 to 35 cc and being adapted for use on a hand-held engine-driven appliance such as a weed-trimmer or the like. 
     
     
       13. In a diaphragm carburetor adapted for mounting and use on an internal combustion engine, and operable for reducing gaseous phase presence in a liquid fuel metering chamber of said diaphragm carburetor, such phase being in the form of air or fuel vapor agglomeration and/or bubble growth due to the same evaporating or effervescing from the liquid fuel during engine running and/or in the form of air when the chamber is not full of liquid fuel and hence air-filled due to carburetor fuel drain-down after engine-shut down, said carburetor having a main air/fuel mixing through passageway, a fuel metering cavity formed in a body part of said carburetor and a metering diaphragm spanning said metering cavity and defining a fuel metering chamber therebetween, a liquid fuel supply passageway coupled between a pressurized source of liquid fuel and said metering chamber, an inlet valve disposed in said supply passage and being operably coupled to said diaphragm for controlling opening and closing of said inlet valve to admit pressurized liquid fuel from the fuel source to the metering chamber in response to pressure differential between atmospheric pressure and engine-intake-induced negative pressure in the carburetor mixing passageway acting on the metering diaphragm, an engine fuel feed metering circuit passageway system having a first inlet operably communicating with the metering chamber and outlet means operably communicating via check valve means with the carburetor mixing passageway for supplying and metering liquid fuel from the metering chamber via the outlet means into the mixing passageway to form therein an air/fuel mixture for operating the engine, and an air purge passageway system including a fuel vapor and air purge passageway having a second inlet operably communicating with the metering chamber and an outlet adapted for operably communicating with a return line leading to the fuel source, said air purge system also including a pump and associated intake and outlet valves operably coupled in said purge passageway for pumping gas and/or liquid from the metering chamber into the return line, the improvement in combination therewith of said first and second passageway inlets being located to communicate with a gaseous phase collection and take off region of the metering chamber to thereby insure that substantially all such gaseous phase presence is removed from the metering chamber by operation of the passageway systems associated with said inlets, said take off region being located at the highest elevation in the metering chamber with the carburetor mounted on the engine and the mounted carburetor and engine together being oriented in the standard operating position of the engine. 
     
     
       14. The carburetor of  claim 13  wherein said first and second inlets are constructed to communicate solely with a single common inlet opening directly into said highest elevation collection and take off region of the metering chamber such that operation of said purge system, before starting the engine, removes substantially all gaseous phase metering chamber contents from the metering chamber and the fuel feed circuit while drawing liquid fuel into the metering chamber to thereby condition the carburetor for engine start-up with the engine oriented in the standard operating position, and such that while the engine is running in the standard operating position, the gaseous phase bubbles released from the liquid fuel, while resident in the metering chamber, are not allowed to become large enough, either singly or by agglomeration, to adversely affect engine performance when they are drawn into the engine via the fuel feed circuit. 
     
     
       15. The carburetor set forth in  claim 13  in combination with an engine comprising a mini-four-stroke-cycle single cylinder engine having an engine displacement in the order of 20 to 35 cc and being adapted for use on a hand-held engine-driven appliance such as a weed-trimmer or the like. 
     
     
       16. The carburetor set forth in  claim 14  wherein said air purge pump comprises a manually operable squeeze bulb operably associated with said pump inlet and outlet valves and defining the variable volume pumping chamber of the air purge system. 
     
     
       17. The carburetor set forth in  claim 16  wherein said squeeze bulb is mounted on said carburetor. 
     
     
       18. The carburetor of  claim 13  wherein said outlet means of said engine fuel feed metering circuit passageway system includes both idle and high speed fuel feeding orifice means both communicating with the metering chamber solely via said first inlet of said fuel feed passageway system. 
     
     
       19. The carburetor of  claim 18  wherein said first and second inlets are constructed to communicate solely with a single common inlet opening directly into said highest elevation collection and take off region of the metering chamber such that operation of said purge system, before starting the engine, removes substantially all gaseous phase metering chamber contents from the metering chamber while drawing liquid fuel into the metering chamber to thereby condition the carburetor for engine start-up with the engine oriented in the standard operating position, and such that while the engine is running in the standard operating position, the gaseous phase bubbles released from the liquid fuel, while resident in the metering chamber, are not allowed to become large enough, either singly or by agglomeration, to adversely affect engine performance when they are drawn into the engine via the fuel feed circuit. 
     
     
       20. The carburetor of  claim 19  in combination with an engine comprising a mini-four-stroke-cycle single cylinder engine having an engine displacement in the order of 20 to 35 cc and being adapted for use on a hand-held engine-driven appliance such as a weed-trimmer or the like. 
     
     
       21. In a diaphragm carburetor adapted for mounting and use on an internal combustion engine, and operable for reducing gaseous phase presence in a liquid fuel metering chamber of said diaphragm carburetor, such phase being in the form of air or fuel vapor agglomeration and/or bubble growth due to the same evaporating or effervescing from the liquid fuel during engine running, said carburetor having a main air/fuel mixing through passageway, a fuel metering cavity formed in a body part of said carburetor and a metering diaphragm spanning said metering cavity and defining a fuel metering chamber therebetween, a liquid fuel supply passageway coupled between a pressurized source of liquid fuel and said metering chamber, an inlet valve disposed in said supply passage and being operably coupled to said diaphragm for controlling opening and closing of said inlet valve to admit pressurized liquid fuel from the fuel source to the metering chamber in response to pressure differential between atmospheric pressure and engine-intake-induced negative pressure in the carburetor mixing passageway acting on the metering diaphragm, an engine fuel feed metering circuit passageway system having a first inlet operably communicating with the metering chamber and outlet means operably communicating via check valve means with the carburetor mixing passageway for supplying and metering liquid fuel from the metering chamber via the outlet means into the mixing passageway to form therein an air/fuel mixture for operating the engine, the improvement in combination therewith of said first passageway inlet being located to communicate with a gaseous phase collection and take off region of the metering chamber to thereby insure that substantially all such gaseous phase presence is removed from the metering chamber by operation of said fuel feed metering circuit passageway system associated with said first inlet, said take off region being located at the highest elevation region in the metering chamber and being predetermined as to such location with the carburetor mounted on the engine and the mounted carburetor and engine together being oriented in the standard operating position of the engine, such that while the engine is running in the standard operating position, the gaseous phase bubbles released from the liquid fuel, while resident in the metering chamber, are not allowed to become large enough, either singly or by agglomeration, to adversely affect engine performance when they are drawn into the engine via the fuel feed circuit. 
     
     
       22. The carburetor set forth in  claim 21  in combination with an engine comprising a mini-four-stroke-cycle single cylinder engine having an engine displacement in the order of 20 to 35 cc and being adapted for use on a hand-held engine-driven appliance such as a weed-trimmer or the like. 
     
     
       23. The carburetor of  claim 21  wherein said outlet means of said engine fuel feed metering circuit passageway system includes both idle and high speed fuel feeding orifice means both communicating with the metering chamber solely via said first inlet of said fuel feed passageway system. 
     
     
       24. The carburetor of  claim 23  in combination with an engine comprising a mini-four-stroke-cycle single cylinder engine having an engine displacement in the order of 20 to 35 cc and being adapted for use on a hand-held engine-driven appliance such as a weed-trimmer or the like.